1. Field of the Invention
The invention relates to energy saving lamps with electronic ballast.
2. Description of the Related Art
Energy saving lamps are conventionally constructed such that the user can exchange them without further measures against conventional incandescent lamps with Edison screw base, bayonet base or the like. For this reason, many energy saving lamps are provided with an Edison screw base, for example, of the size E 27/30.
DE-A 3611 611 discloses a standard circuit for the electronic ballasts. The following components can be differentiated: power rectifier with suppressing member and charging capacitor, inverse rectifier with two switching transistors and an oscillating circuit transformer with three metallically separated coils, lamp series reactor and gas discharge lamp.
The electric and electronic components of the ballast are conventionally placed onto a printed board with printed conductors.
In order to keep the energy saving lamp as compact as possible, it is generally attempted to integrate the electronic ballast into the lamp. However, there are two great obstacles for the required miniaturization.
The first obstacle are the high voltages to which the electronic device is exposed. These are alternating current supply voltages of 230 V, the direct current supply voltage of 400 V, and the lamp supply voltage which has values of 1,500 V and more before the ignition of the gas discharge.
The greatest obstacle, however, is the heat which is emitted by the electronic components of the ballast. Primarily, this concerns the switching transistors which, as a result of the relatively high oscillation frequency of 20 to 80 kHz, reach housing temperatures of approximately 140xc2x0 C. Heat also is produced in the various reactors since they must be wound with wires of reduced thickness because of the required miniaturization. A further heat source is the magnetic stray fields which are emitted by the reactors, in particular, the series reactors of the lamp, and which induce in the neighboring metal parts, for example, the lamp base, corresponding short-circuit currents. Finally, the gas discharge lamp, in particular, its heating electrodes, also produces heat. The result of the described obstacles is that the electronic ballasts of the conventional energy saving lamps at least partially are seated externally to the lamp base and thus enlarge the constructive length, possibly also the diameter, of the energy saving lamps to a considerable extent in comparison to conventional incandescent lamps.
The present invention has the object to improve and further develop the known energy saving lamps such that the electronic ballast can be completely housed in a standard lamp base.
The solution according to the invention resides in a plurality of measures which enhance one another in order to thus achieve the set goal of housing the electronic ballast completely in the lamp base, preferably in a screw fitting of the size E 27.
Since the main problem, as described above, is the heat development, first a suitable heat sink was searched for the switching transistors and was indeed found in the form of the metallic outer contact part of the lamp base. The switching transistors are thus arranged on the printed board such that their heat can be transmitted well onto the metal parts of the lamp base. Preferably, the switching transistors are arranged such that their cooling bodies rest against the base insulator of the lamp base so that special insulating measures are obsolete.
While in the known energy saving lamps the printed board is positioned external to the lamp base, pursuant to the solution according to the invention it is positioned directly within the lamp base. Here it is secured by means of a special inner lid which is placed on top of the lamp base, preferably is non-detachably snapped onto it.
For this purpose, the lamp base according to a further development has at its upper edge several, preferably four, penetrations, and the inner lid an edge with corresponding locking cams. In this way it is ensured that the inner lid cannot be removed accidentally. The electrical safety is thus ensured.
Preferably, the inner lid is configured such that it tightly closes off the lamp base. Accordingly, the electronic components as well as the conductors of the printed board are protected against damaging effects of air pollutants, air moisture and the like.
According to an embodiment of the invention, the inner lid is metallized at the exterior. This metallization acts as a shield and at the same time as a light reflector.
An especially space-saving, assembly cost-saving, and assembly time-saving solution was realized for an oscillating frequency transformer and its three metallically separated coils. The annular core has a flat rectangular shape and is seated in a matching recess in the printed board. The three coils are configured as printed conductors, wherein a semi-winding is positioned on the printed board and the corresponding second semi-winding on an additional board, respectively. The oscillating circuit transformer is completed in that the additional board is inserted upside-down through the annular core and is placed onto the printed board. After soldering of the corresponding semi-windings the transformer is complete. At the same time, the annular core is fixed on the printed board.
Also, the shape and arrangement of the lamp ballast contributes to the miniaturization of the electronic ballast. An open ferrite body is used as the coil body so that the wire windings can be applied very simply. The wound coil body is then inserted into a recess preferably at the upper edge of the printed board and glued thereto. In this way, the lamp ballast has a maximum spacing to the metal parts of the lamp base and a minimal spacing to the gas discharge lamp.
However, it was found that the lamp ballast produces considerable stray fields which induce in the metal parts of the lamp base considerable short-circuit currents. For this reason, a U-shaped magnet core is additionally provided which covers with a sufficient air gap the wound ferrite coil body. This U-shaped core reduces the stray fields of the reactor. At the same time, it provides the possibility of changing the inductivity and thus the alternating current resistance of the series reactor during the production in a targeted way so that gas discharge lamps of different power can be operated on otherwise identical ballasts.
In addition, a two-sided metallization of the printed board also contributes to the miniaturization of the electronic ballast.
In all energy saving lamps the gas discharge lamp, which, as is known, is comprised of one or more gas tubes usually folded in a U-shape, must be mechanically securely and permanently connected to the lamp base. For this purpose, conventionally a base insert of insulating material is used which is, on the one hand, connected to the lamp base and on which, on the other hand, the gas discharge lamp is fastened, generally by means of a so-called cement.
In the energy saving lamp according to the invention such a base insert is also used. It is of a two-part configuration wherein the lower part according to an advantageous embodiment has a central opening whose diameter is larger than the diameter of the outer contact part but smaller than the diameter of the edge of the lamp base.
In the case that a so-called glass envelope is to be placed about the gas discharge tube, for example, in the shape of an incandescent lamp, the gas discharge lamp can also be attached in the following way.
According to a further development, a securing device is provided on the inner lid which matches the shape and length of the glass tube or glass tubes of the gas discharge lamp and secures it by clamping. It is understood that the springy elements of the securing device are positioned at the center of the gas discharge lamp so that the radiation of the light is not impair.
The permanent attachment between the gas discharge lamp and the securing device on the lid can be realized with a suitable adhesive.
According to a preferred configuration of the invention, an additional securing bracket is provided which secures the gas discharge lamp, for example, in the area of the so-called hotkiss. On the inner lid additional devices are then provided on which the securing bracket is anchored.
Further embodiments of the invention are the subject matter of the remaining dependent claims.